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However, according to Bill Gates, many of these new toilets don't get used because they smell bad, and people continue to relieve themselves in the open where the air is fresher.

"This is a worrying trend that threatens to undermine the progress that's been achieved in global sanitation," said Gates in on his Gates Notes blog .

(Image: YouTube/thegatesnotes)

While pleasant fragrances are often used to cover over the malodors we want to hide - the olfactory equivalent of sweeping dirt under a rug - Firmenich decided to try a different, more innovative approach.

With funding from the Gates Foundation, it managed to isolate the four chemical compounds that are responsible for the terrible smell in toilets, and then recreate the odour using synthetic compounds.

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Firmenich researchers then used the "poop perfume" to develop fragrances that block certain olfactory receptors in our noses, making us unable to register these bad smells.

(Image: YouTube/thegatesnotes)

The approach is similar to noise-cancelling headphones which many people use to block out jet engine noise on flights. Electronics in the headsets create a sound wave that is 180 degrees out of phase with the engine noise - effectively cancelling it out.

Likewise, the ingredients in the fragrances developed by Firmenich inhibit the activation of the olfactory receptors sensitive to malodors. By blocking the receptors, our brains do not perceive the bad smells.

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"I had an opportunity to experience the odour-blocking fragrances in action. I was invited to push my nose into a glass sniffing tube and breathe in a mixture of the poop perfume I had just experienced and one of the new odor-blocking fragrances," said Gates.

(Image: YouTube/thegatesnotes)

"It smelled pretty good. There was no evidence of repulsive odor I had experienced earlier. Instead of stinky sewage, sweat, and ripe cheese, I sniffed a pleasant floral scent."

Firmenich is now launching pilot projects in communities across India and Africa to understand whether the fragrances will make toilets and pit latrines more inviting for users.

They also need to determine if it's better to distribute the fragrance as a spray, a powder, or something else. The ultimate goal is to make the product affordable and easy-to-use, according to Gates.